While not every 13-year-old is on social media, or wants to be, many are. Fifty-seven percent of 13- and 14-year-olds use Facebook, 44 percent use Instagram, and 21 percent use Twitter, according to the Pew Research Center. And as 13-year-olds begin to mix social media into their lives, they open a window into the carefully curated lives of their classmates. Many are delighted by that additional connection, but even the most socially deft teenagers can feel left out of pictured fun that doesn’t include them, get caught up in online conflict, or feel slighted by a lack of appreciation of their posts. For young teenagers who are experiencing less offline social success, the online world can exacerbate their difficulties.

“Students who are comfortable socially in offline interactions seem to know exactly how to use social media to get a lot of support and affirmation online,” said Marion Underwood, dean of graduate studies in the School of Behavioral and Brain Sciences at the University of Texas at Dallas and a co-author of the “Being 13” report. Social media seems to amplify young adolescents’ personality characteristics rather than changing them. “It’s a situation where the rich get richer, and the poor get poorer,” Dr. Underwood said.

Dr. Underwood and her colleagues looked at the archived social media posts of over 200 13-year-olds from six states from September 2014 to April 2015. Participating students downloaded an app that would record all posts and photos and responded to a survey. Their parents were surveyed as well. What these researchers found was largely consistent with recent reports from the Pew Foundation, which suggested that most teenagers 13 to 17 were generally happy with their connected lives online, and believed that hanging out virtually strengthened their offline relationships.

“Being 13” provides an asterisk of sorts to that rosy outlook: These teenagers, at the youngest end of the spectrum, valued their online connectedness but also described in more detail the ways the specific online interactions affected them. Although much of that impact, even when negative, appears to be short-lived (researchers found no meaningful associations between involvement with social media and psychological adjustment), many of the individual comments and behaviors from teenagers suggested that social media had great power to affect their day-to-day emotions in ways a parent might regard with suspicion. One child said she took 100 to 200 pictures of herself to get a good selfie; another regularly posted images on Instagram seeking specific forms of approval only to receive silence in return. Many spent hours scrolling through the images of their peers’ lives online.

Among the most positive results of the research was the importance of parental involvement for this age group. “Children who felt like their parents were monitoring their activity online were noticeably less distressed by online conflict,” Dr. Underwood said. “Children perceive that their parents care about their online lives, and they’re probably talking about them.”

Here’s how to guide, help and monitor your child as she joins social media.

Agree on boundaries. If your child is 13 or older and interested in joining social media, Dr. Underwood says she should be allowed to try it out. She suggests asking your child what her goals are and why she wants to join, and talking about making it a positive experience. Discuss the negatives: Not only should she be aware that her posts affect others, she should also know how the posts of others can affect her. Work with her to set some rules — no phones in the bedroom at night, no phones at the dinner table — tell her you’ll be friending or following her, and plan to check back in after a few weeks to see how it’s going.

Start with Instagram. Dr. Underwood calls the photo-sharing site a benign, simpler service. “Kids care a lot about putting funny positive things on Instagram,” she says, and most stick to the site’s unwritten etiquette, posting only once a day but commenting far more frequently. Show them how it works, she says, set up the account together and set the privacy settings. She suggests adding Facebook next and avoiding Twitter if possible. Because of its “blurt out whatever’s in your head” nature, she saw more negative behavior on Twitter by the teenagers in the study than on the other platforms.

Watch for lurking. As Dr. Underwood and her co-author, Robert W. Faris, described in an editorial for CNN, more than one-third of the teenagers in their study said they check social media, without posting, 25 times or more per day on weekends. The heaviest users said they used social media over 100 times daily, including during classes at school. Teenagers who spend more time lurking are more likely to see and be distressed by social media posts about friends doing things together without them, and more likely to compare their own real experiences to “everyone else’s filtered, carefully selected pictures chosen to be the most positive depiction of themselves having a marvelous time.”

“If you see them using their phone more than is usual, really glued to Twitter or Instagram, show an interest,” Dr. Underwood suggested. “Ask them what’s happening.”

If your child admits to feeling left out or hurt by someone’s online behavior, first, consider yourself lucky — you’re talking. Next, “Your first and most important job is to be a listener,” said Betsy Brown Braun, a child development and behavior specialist and the author of “Just Tell Me What to Say: Sensible Tips and Scripts for Perplexed Parents.” “Hear her out. Validate and empathize without being fake or corny.”

If other children are involved, she said, “rather than being critical of others (as kids’ relationships fluctuate fast) help the child to come up with ideas and choices about what to do.” You are a consultant, she says, not a director.

If the teenager is feeling overwhelmed by the seemingly perfect lives of others, talk about how curated those images are, and encourage your child to spend less time scrolling her feed if it’s not making her happy. “The No. 1 reason teenagers say they spend time lurking online is boredom,” Dr. Underwood said. “Maybe arrange for them to be a little less bored.”

But lurk yourself. “Your job,” Dr. Underwood said, “is to be the silent, watchful friend. ‘Like,’ if you want, but don’t comment. You don’t want to be a real presence on your child’s social media.” But you do want to be aware of what’s posted and said. “You’re a second set of eyes,” said Ms. Braun, for a child who may not know what isn’t safe, or may not think about what might be hurtful to others.

Don’t overdo the watchfulness, however. Let her make her own mistakes; don’t rush to assume something has hurt or offended her. Keeping the tone of your monitoring light will make it more acceptable to your child, and give your concerns more weight if you do need to say something.

Don’t rely on your child’s own posts. “You never want to rely on what they’re posting as the only barometer of how they’re doing,” Dr. Underwood said. It’s easy to see your child post a perfect picture and assume she is having a perfect night, but just like her peers, your child is putting out her most perfect self, and responding to others as that self. “The most vigilant parent could read every word of a child’s feed and still not detect hurtful behavior,” she said. So ask your child how she’s feeling about what’s happening online rather than relying on her emojis.

Share your own experiences. If you have felt excluded, inadequate or just out of it while reading your own social media feeds, tell your child about it, Ms. Braun suggests. You could even sit down with your own Facebook together and take note of the friend who just won a half-marathon or the one whose book is on the best-seller list, and the picture of six other parents enjoying a boat ride — without you. “This way when (and not if) something happens and the child feels bad, first of all, it won’t be unfamiliar,” she said. “Second, she will be likely to come to you to talk and for support.”

Expect mistakes, and don’t expect your child to be you. “At 13, it’s really cool to post lots of pictures of yourself having fun with friends,” Dr. Underwood said. “As they get older, that’s a little uncouth, the response is like, why are you doing this, are you desperate to show you have friends? I think they get more cognitively sophisticated and aware of their impact on other people. But at 13, they’re so excited to be on social media. There’s a developmental difference in how teenagers use these things.” And different children want different things from social media. “They may not care if they get three likes or if they follow a bunch of people who don’t follow them,” she said.

Or they might care a lot. “How great would it be if we could immunize our kids (and ourselves) from getting our feelings hurt or feeling bad?” Ms. Braun said. “It just can’t be done. But through these sometimes dreadful and painful experiences, great social and emotional learning and growth happens.”

Being 13 has always meant walking a tightrope between adolescence and childhood, between self-awareness and self-absorption, between being yourself and being the person you hope others will see. Social media may have amplified that balancing act, but it didn’t create it, and now, it’s just one more rite of passage — and one more chance for parents to strike a balance between guiding children and letting them find their own way.

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We're all living the family dynamic, as parents, as children, as siblings, uncles and aunts. At Motherlode, lead writer and editor KJ Dell’Antonia invites contributors and commenters to explore how our families affect our lives, and how the news affects our families—and all families. Join us to talk about education, child care, mealtime, sports, technology, the work-family balance and much more